Low application temperature elastic attachment adhesive

ABSTRACT

Low application temperature thermoplastic hot melt adhesives are particularly useful as elastic attachment adhesives. The adhesives have a viscosity at 275° F. of less than about 8,000 cp, a yield stress of less than about than 80 psi and a creep performance for a bond made through strand coating of less than about 15%. Preferred are adhesives that have a creep performance for a bond made through spiral coating of less than about 25%.

The benefit of the earlier filing dates of PCT/US2005/002905, filed Jan.31, 2005, and U.S. application Ser. No. 10/773,542, filed Feb. 2, 2004,is claimed.

FIELD OF THE INVENTION

The present invention relates to low application temperature hot meltadhesive compositions that are particularly well suited for elasticattachment applications.

BACKGROUND OF THE INVENTION

Hot melt adhesives are widely used for various commercial and industrialapplications such as product assembly and packaging. Such hot meltadhesives are applied to a substrate while in its molten state andcooled to harden the adhesive layer.

Most commercially available hot melt adhesives require temperatures of350° F. or greater to ensure complete melting of all the components andalso to achieve a satisfactory application viscosity. The need for suchelevated temperatures is not without problems. The high temperaturesincrease operators risks with respect both to burns and to inhalation ofresidual volatiles. In addition, the high temperatures require moreenergy, placing greater demands on the manufacturing facility.

Adhesive formulations, which can be applied at temperatures below 300°F., can be prepared using low polymer/elastomer content or low molecularweight components or a high wax content. Although these formulationsachieve a low application viscosity, there is a resulting loss ofadhesive properties such as toughness, heat resistance, and sometimes,specific adhesion to a substrate. While the formulation ofpoly(ethylene-vinylacetate)-based adhesives having high heat resistancehas been in addressed in the art, see, e.g., U.S. Pat. No. 6,117,945,lower application temperature (e.g., less than 300° F.) thermoplasticelastomer-based adhesives which provide toughness, strength, andspecific adhesion on a desired substrate have not been achieved.

Accordingly it would be desirable to have thermoplastic elastomer-basedadhesives that exhibit good bond strength with exceptional toughness,tensile strength and application viscosity, even if prepared with lowmolecular weight components for application at low temperatures. Thecurrent invention addresses this need in the art.

SUMMARY OF THE INVENTION

The invention provides an adhesive that can be applied at lowertemperatures, for example at temperatures of from about 200 to about300° F., yet still provide exceptional toughness. The adhesives of theinvention are particularly useful in elastic attachment applications innon-wovens, e.g., as used in the manufacture of baby diapers, trainingpants and adult incontinence garments.

One aspect of the invention is directed to low application temperaturethermoplastic hot melt adhesive having a viscosity at 275° F. of lessthan about 8,000 centipose (cp), a yield stress of less than about 80pounds per square inch (psi) and a creep performance for a bond madethrough strand coating of less than about 15%. In preferred embodiments,the adhesive has a creep performance for a bond made through spiralcoating of less than about 25%. The adhesive may, if desired, contain anamount of an additive effective to lower viscosity and/or increasestoughness.

One embodiment of the invention provides an adhesive comprising fromabout 0.5 to about 55 wt % of a thermoplastic elastomer, from about 30to about 90 wt % of a tackifying resin, from 0 to about 40 wt % of adiluent and from 0 to about 25 wt % of a wax and from 0 to about 40 wt %of an additive that lowers the viscosity and/or increases toughness, theadhesive having a viscosity at 275° F. of less than about 8,000 cp, ayield stress of less than about than 80 psi and a creep performance fora bond made through strand coating of less than about 15%. Preferredadhesives of the invention will have a creep performance for a bond madethrough spiral coating of less than about 25%. A particularly preferredadditive for use in the practice of the invention is an ionomer.

Another aspect of the invention is directed to an article of manufacturecomprising a low application temperature thermoplastic hot melt adhesivehaving a viscosity at 275° F. of less than about 8,000 cp, a yieldstress of less than about than 80 psi and a creep performance for a bondmade through strand coating of less than about 15%. In one embodiment,the adhesive will have a creep performance for a bond made throughspiral coating of less than about 25%. Articles of manufacture willtypically comprise at least one substrate. In one embodiment, thearticle of manufacture is a diaper comprising such an adhesive. Theadhesives find particular use in elastic attachment applications in themanufacture of articles comprising an elastic region, such as is foundin disposable absorbent garments comprising one or more elastic cuffspositioned to contact the legs and/or waist of the wearer. In aparticularly preferred embodiment, the elastic substrate comprisesspandex.

Still another aspect of the invention is directed to a process forbonding a substrate to a similar or dissimilar substrate comprisingapplying to at least a first substrate a molten hot melt adhesivecomposition, bringing at least a second substrate in contact with theadhesive present on the first substrate whereby said first and secondsubstrates are bonded together. The adhesive composition used in theprocess is a low application temperature thermoplastic hot melt adhesivehaving a viscosity at 275° F. of less than about 8,000 cp, a yieldstress of less than about than 80 psi and a creep performance for a bondmade through strand coating of less than about 15%. In one embodiment,the adhesive has a creep performance for a bond made through spiralcoating of less than about 25%. In a particularly preferred embodiment,at least one substrate is an elastomeric polyurethane fiber (spandex).Another preferred embodiment is directed to a process for bonding atissue or a nonwoven substrate to a similar or dissimilar substrate inthe construction of a disposable absorbent product.

DETAILED DESCRIPTION OF THE INVENTION

All documents cited herein are incorporated in their entireties byreference.

The present invention provides a low application temperaturethermoplastic hot melt adhesive composition. Compositions of theinvention can be applied at temperatures between from about 200 to about300° F. yet still provide exceptional toughness and specific adhesions.In one embodiment, the adhesive is applied at a temperature above about250° F., preferably at a temperature of from about 270° F. to about 285°F. In another embodiment, the adhesive can be applied at temperatures of250° F., down to about 200° F. Hot melt adhesives that can be applied atlow temperatures (from about 300° F. down to about 200° F.) areparticularly useful as elastic attachment adhesives since many fiberscan be stretched further, without breakage, than when using aconventional hot melt adhesive.

One property that is particularly desirable when the adhesive is to beused in elastic attachment applications, is creep performance. In suchapplications, an adhesive with excellent toughness is preferred. Theadhesives of the invention have those properties desired for elasticattachment applications, and other applications. The adhesives areparticularly useful in making elastic non-wovens and in the fabricationof baby diapers, training pants, adult incontinence briefs orundergarments, and the like.

Adhesives encompassed by the invention are low application temperatureadhesives having a viscosity at 275° F. of less than about 8,000 cp, ayield stress of less than about than 80 psi and a creep performance fora bond made through strand coating of less than about 15%. In onepreferred embodiment, the adhesive will have a creep performance for abond made through spiral coating of less than about 25%, more preferablyless than about 20%, even more preferably less than about 18%.Determination of creep performance can be made as described in theExamples.

The low application temperature hot melt adhesives of the inventioncomprise a thermoplastic elastomer, a tackifying resin and, if desired,other additives such as diluents, waxes and the like. A preferredadditive is an additive that lowers the viscosity and/or increasestoughness such that the adhesive has a viscosity at 275° F. of less thanabout 8,000 cp, a yield stress of less than about than 80 psi and acreep performance for a bond made through strand coating of less thanabout 15%. A particularly preferred additive is an ionomer resin. Aparticularly preferred adhesive will comprise at least one ionomer andwill have a creep performance for a bond made through spiral coating ofless than about 25%.

An adhesive encompassed by the invention typically comprises from about0.5 to about 55 wt %, preferably from about 5 to about 55 wt %, of atleast one thermoplastic elastomer. Polymers that may be used inpreparing the thermoplastic elastomer component of the adhesivecompositions of the present invention are block copolymers having thegeneral configuration A-B-A wherein the polymer end-blocks A arenon-elastomeric polymer blocks which, as homopolymers, have glasstransition temperatures above about 20° C., while the elastomericpolymer mid-blocks B are derived from isoprene, butadiene or isobutylenewhich may be partially or substantially hydrogenated or mixturesthereof. Further, the block copolymers may be linear or branched.Typical branched structures contain an elastomeric portion with at leastthree branches that can radiate out from a central hub or can beotherwise coupled together.

The non-elastomeric end-blocks A may comprise homopolymers or copolymersof vinyl monomers such as vinyl arenes, vinyl pyridines, vinyl halidesand vinyl carboxylates, as well as acrylic monomers such asacrylonitrile, methacrylonitrile, esters of acrylic acids, etc.Monovinyl aromatic hydrocarbons include particularly those of thebenzene series such as styrene, vinyl toluene, vinyl xylene, and ethylvinyl benzene as well as dicyclic monovinyl compounds such as vinylnaphthalene and the like. Other non-elastomeric polymer blocks may bederived from alpha olefins, alkylene oxides, acetals, urethanes, etc.Styrene is preferred.

The elastomeric mid-block B component making up the remainder of thethermoplastic elastomeric copolymer is typically derived from isoprene,butadiene or isobutylene which may be hydrogenated as taught, forexample, in U.S. Pat. No. 3,700,633. This hydrogenation of butadiene maybe either partially or substantially complete. Selected conditions maybe employed for example to hydrogenate the elastomeric butadiene blockwhile not so modifying the vinyl arene polymer blocks. Other conditionsmay be chosen to hydrogenate substantially uniformly along the polymerchain, both the elastomeric and non-elastomeric blocks thereof beinghydrogenated to practically the same extent, which may be either partialor substantially complete. Hydrogenated polymers are preferred tominimize degradation during processing, which can be a more severeproblem with higher molecular weight polymers.

The adhesives of the invention will typically comprise from about 30 toabout 90 wt % of a tackifying resin. Preferred adhesives will comprisefrom about 40 to about 80 wt %, more preferably from about 40 to about65 wt % of a tackifying resin which is compatible with the midblock ofthe thermoplastic elastomer. Preferred are mid-block tackifying resinshaving a Ring and Ball softening point above about 25° C. Suitablemid-block tackifying resins include any compatible resins or mixturesthereof such as (1) natural or modified rosins such, for example, as gumrosin, wood rosin, tall-oil rosin, distilled rosin, hydrogenated rosin,dimerized rosin, and polymerized rosin; (2) glycerol and pentaerythritolesters of natural or modified rosins, such, for example as the glycerolester of pale, wood rosin, the glycerol ester of hydrogenated rosin, theglycerol ester of polymerized rosin, the pentaerythritol ester ofhydrogenated rosin, and the phenolic-modified pentaerythritol ester ofrosin; (3) copolymers and terpolymers of natural terpenes, e.g.,styrene/terpene and alpha methyl styrene/terpene; (4) polyterpene resinshaving a softening point, as determined by ASTM method E28,58T, of fromabout 800 to 150° C.; the latter polyterpene resins generally resultingfrom the polymerization of terpene hydrocarbons, such as the bicyclicmonoterpene known as pinene, in the presence of Friedel-Crafts catalystsat moderately low temperatures; also included are the hydrogenatedpolyterpene resins; (5) phenolic modified terpene resins andhydrogenated derivatives thereof, for example, as the resin productresulting from the condensation, in an acidic medium, of a bicyclicterpene and phenol; (6) aliphatic petroleum hydrocarbon resins having aBall and Ring softening point of from about 70° to 135° C.; the latterresins resulting from the polymerization of monomers consisting ofprimarily of olefins and diolefins; also included are the hydrogenatedaliphatic petroleum hydrocarbon resins; (7) alicyclic petroleumhydrocarbon resins and the hydrogenated derivatives thereof; and (8)aliphatic/aromatic or cycloaliphatic/aromatic copolymers and theirhydrogenated derivatives.

Preferred mid-block tackifying resins for use herein includepolyterpenes such as Wingtack 95 from Goodyear; aliphatic resins such asHercures C from Hercules; cycloaliphatic resins such as Eastotac H100Rfrom Eastman; and aliphatic/aromatic or cycloaliphatic/aromatic resinssuch as ESCOREZ 5600 from ExxonMobil Chemical Company. More preferredare the aliphatic and cycloaliphatic resins. The desirability andselection of the particular tackifying agent can depend upon thespecific elastomeric block copolymer employed.

Additionally, it may be desirable to incorporate in the adhesive up toabout 30 wt % of an end block tackifying resin. End block tackifyingresins reside predominantly in the non-elastomer blocks of thethermoplastic elastomer after the adhesive is cooled. Representative ofsuch resins are the primarily aromatic resins based on mixed C9petroleum distillation streams such as the Hecures materials availablefrom Hercules, or resins based on pure or mixed monomer streams ofaromatic monomers such as homo or copolymers of vinyl toluene, styrene,alpha-methyl styrene, coumarone or indene. Preferred are those based onalpha-methyl styrene available from Hercules under the Kristalex tradename. If present, the end block tackifying resin is generally used in anamount of from about 5 to about 30 wt %, preferably less than about 20wt %.

There may also be present in the adhesive up to about 40 wt %,preferably about 5 to about 30 wt %, of an oil or other liquid diluentwhich is primarily aliphatic in character and is compatible with thethermoplastic elastomer midblock. Examples include plasticizers such asparaffinic and naphthenic petroleum oils, highly refined aromatic-freeparaffinic and naphthenic food and technical grade white petroleummineral oils, and liquid tackifiers such as the synthetic liquidoligomers of polybutene, polypropene, polyterpene, etc. The syntheticseries process oils are high viscosity oligomers which are permanentlyfluid liquid monolefins, isoparaffins or paraffins of moderate to highmolecular weight. Liquid plasticizing or tackifying diluents includepolyterpenes such as Wingtack 10 available from Goodyear, and Escorez2520 based on a C₅ feed stream available from Exxon Chemical. Otherliquid diluents include polyisoprene, available as LIR 50 from Kuraray,and Amoco's polybutenes available under the name Indopol. Most preferredare paraffinic oils in combination with Escorez 2520, a polymerized C₅petroleum feed stream.

Also, optionally, there may be present up to about 25 wt %, preferablyup to about 5 wt %, of a wax. Waxes suitable for use in the presentinvention include paraffin waxes, microcrystalline waxes, polyethylenewaxes, polypropylene waxes, by-product polyethylene waxes,Fischer-Tropsch waxes, oxidized Fischer-Tropsch waxes and functionalizedwaxes such as hydroxy stearamide waxes and fatty amide waxes. It iscommon in the art to use the terminology synthetic high melting pointwaxes to include high density low molecular weight polyethylene waxes,by-product polyethylene waxes and Fischer-Tropsch waxes. Modified waxes,including vinyl acetate modified waxes such as AC-400 (Honeywell) andMC-400 (available from Marcus Oil Company), maleic anhydride modifiedwaxes such as Epolene C-18 (available from Eastman Chemical) and AC-575Aand AC-575P (available from Honeywell) and oxidized waxes may be used inthe practice of the invention. Particularly preferred are polyethylenewaxes. If used, the wax is generally present in an amount of at leastabout 2 wt %.

One embodiment of the invention provides an adhesive comprising fromabout 0.5 to about 55 wt % of a thermoplastic elastomer, from about 30to about 90 wt % of a tackifying resin, from 0 to about 40 wt % of adiluent and from 0 to about 25 wt % of a wax and an amount of anadditive effective to lower the viscosity and/or increase toughness ofthe adhesive. The additive containing adhesive has a viscosity at 275°F. of less than about 8,000 cp, a yield stress of less than about than80 psi and a creep performance for a bond made through strand coating ofless than about 15%. Preferred adhesives of the invention will have acreep performance for a bond made through spiral coating (unwrapped) ofless than about 25%, more preferably less than about 20%, even morepreferably less than about 18%.

Whether a particular additive is effective to lower viscosity orincrease toughness of an adhesive can be determined by the skilledpractitioner using the tests described in the examples. In accordancewith the invention, the additive is used in an amount effective toprovide an adhesive having a viscosity at 275° F. of less than about8,000 cp, a yield stress of less than about than 80 psi and a creepperformance for a bond made through strand coating of less than about15%. In a preferred embodiment, addition of the additive provides anadhesive having has a creep performance for a bond made through spiralcoating of less than about 25%. Preferably, the amount of additive usedis such that it replaces a like portion of the thermoplastic elastomercomponent of an adhesive formulation which lacks such additive.

A particularly preferred additive for use in the practice of theinvention is an ionomer resin. Adhesives comprising an ionomer willpreferably comprise up to about 40 wt %, typically from about 0.1 wt %to about 40 wt %, more typically from about 0.1 wt % up to about 15 wt%, more typically less than about 10 wt %, even more typically up toabout 5 wt % of an ionomer resin or mixture thereof. Useful ionomers arepolymers or copolymers of compounds that contain, but are not limitedto, carboxylate, sulphonate or phosphonate that is neutralized orpartially neutralized by Na⁺, Li⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, Ba⁺⁺ or Al⁺⁺⁺ orother metallic ions. The percentage of the ionic content in thecopolymer can be varied and the percentage of neutralization can also bevaried. Ionomers for use in the practice of the invention arecommercially available. For example, there are acrylic acidbased-ionomers, such as ACLyn® from Honeywell, Surlyn® from DuPont, andEscor® and Iotek® from ExxonMobil, that are copolymers of ethylene andacrylic acid or methacrylic acid neutralized by metallic ions. Alsoavailable are butadiene-styrene-acrylic acid terpolymer such as Hycar®from B. F. Goodrich. Useful ionomers include perfluorinated ionomers.Such ionomers are commercially available. Examples include DuPont'sNafion®, and Asahi Glass Company's Flemion®.

Finally, antioxidants typically used in the production of rubber basedpressure sensitive adhesives may be present in an amount of up to about3 wt %. Among the useful stabilizers or antioxidants utilized herein areincluded high molecular weight hindered phenols and multifunctionalphenols such as sulfur and phosphorous-containing phenols. Hinderedphenols are well known to those skilled in the art and may becharacterized as phenolic compounds which also contain sterically bulkyradicals in close proximity to the phenolic hydroxyl group thereof. Inparticular, tertiary butyl groups generally are substituted onto thebenzene ring in at least one of the ortho positions relative to thephenolic hydroxy group. Representative hindered phenols include:1,3,5-trimethyl 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene;pentaerythrityltetrakis-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate;4,4′-methylenebis(2,6-tert-butylphenol);4,4′-thiobis(6-tert-butyl-o-cresol); 2,6-di-tert-butylphenol;6-(4-hydroxyphenoxy)-2,4-bis(n-octylthio)-1,2,5-triazine;di-n-octadecyl3,5-di-tert-butyl-4-hydroxybenzyl phosphonate;2-(n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxybenzoate; and sorbitolhexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate].

The adhesives of the present invention may be prepared using techniquesknown in the art. Typically, the adhesive compositions are prepared byblending the components in the melt at a temperature of about 100° to200° C. until a homogeneous blend is obtained. Various methods ofblending are known and any method that produces a homogeneous blend issatisfactory.

A preferred low application temperature hot melt adhesive compositioncomprises (a) from about 5 to about 35 wt % of a thermoplastic elastomersuch as styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS),styrene-isobutylene styrene (SIBS),styrene-b-ethylene/butylene-b-styrene (SEBS), and/orstyrene-b-ethylene/propylene-b-styrene (SEPS), or radial copolymer(SI)_(n), and/or (SB)_(n), wherein n is equal or larger than 3, (b) fromabout 40 to about 70 wt % of a tackifying resin which is compatible withthe mid-block of the block-copolymer listed in (a), (c) from about 5 toabout 30 wt percent of a thermoplastic hydrocarbon tackifying resinwhich is compatible with the end-block of the block-copolymer listed in(a), (d) from about 0.1 to about 15 wt percent of an ionomer resin, (e)from 0 to about 30 wt % of a diluent such as mineral oil and (f) from 0to about 5 wt % wax, and will have a viscosity at 275° F. of less thanabout 8,000 cp, a yield stress of less than about than 80 psi and acreep performance for a bond made through strand coating of less thanabout 15%. In preferred embodiments, the adhesive has a creepperformance for a bond made through spiral coating of less than about25%. Preferably, the amount of additive used is such that it replaces alike portion of the thermoplastic elastomer component of an adhesiveformulation which lacks such additive.

The adhesive may be applied to a desired substrate by any method knownin the art, and include, without limitation roll coating, painting,dry-brushing, dip coating, spraying, slot-coating, swirl spraying,printing (e.g., ink jet printing), flexographic, extrusion, atomizedspraying, gravure (pattern wheel transfer), electrostatic, vapordeposition, fiberization and/or screen printing.

The adhesive of the invention are useful as positioning adhesives, coreadhesives or elastic adhesives, and are particularly suitable for use inthe manufacture of articles, including but not limited to disposableabsorbent articles, such as diapers, adult incontinent products, bedpads; sanitary napkins, and in other absorbent products, such as, bibs,wound dressings, and surgical capes or drapes, which are used to absorba liquid, such as water and saline, and body liquids, such as urine,menses, and blood. The adhesive may be used to adhere a nonwoven ortissue to another substrate or component. The second substrate may beanother nonwoven, tissue, or an unrelated material.

The present invention provides an absorbent article of manufacturecomprising a liquid permeable topsheet, a liquid impermeable back sheetand an absorbent member interposed between the topsheet and the backsheet. Typically, the back sheet will be a composite sheet comprising aliquid impermeable sheet and a nonwoven fabric joined to each other byan adhesive. The invention encompasses composites and disposableabsorbent products made with or with out one or more elastomeric strandsor ribbons.

As an absorbent structure or product is made, it generally undergoes anumber of different steps in which components or pieces are connected toone another. For example, portions of the topsheet and backsheettypically are bonded together. Also, to the extent the absorbentstructure or product incorporates elastomeric regions such aselasticized waistbands or elasticized leg bands or leg cuffs, elasticstrands or elastic ribbons are typically bonded to a portion of one ormore base materials, substrates, or webs.

“Bonded” or “attached” refers to the joining, adhering, connecting, orthe like, of two elements. Two elements are considered bonded togetherwhen they are bonded directly to one another or indirectly to oneanother (e.g., as when each element is directly bonded to anintermediate element).

Piece” or “component,” as used herein, means a discrete part, a web, orsome other element used to help build a composite or an absorbentproduct. Examples of such discrete parts or webs are discussed below.

“Elastic strand,” as used herein, means a strand comprising polymericconstituents such as, but not limited to: polyetherester; polyurethane;polyamide; or combinations thereof, including random, block, or graftcopolymers such as polyester-b-polyurethane block copolymers,polyether-b-polyurethane block copolymers, styrenic block copolymers,and/or polyether-b-polyamide block copolymers. Examples of elasticstrand include LYCRA, a multifilament elastomeric thread sold byInvista, Inc., and GLOSPAN, an elastic strand made by GlobeManufacturing Company.

For those composites comprising an elastic strand, elastic ribbon, orother elastomeric material, “creep-resistance” or “creep-resistancevalue” refers to the elastic-strand holding power of a particular systemfor attaching one or more elastic materials to at least one piece. Forexample, if an adhesive is applied in liquid form to a first piece, andan elastic strand or strands are then pressed against the adhesive andfirst piece to attach the strand or strands to the first piece, thencreep resistance is a measure of the quality of the adhesive bondbetween the strand or strands and the first piece. Generally the elasticstrand or strands will be sandwiched between a first piece and a secondpiece, or will be enclosed by folding a piece over the strands.

The term “nonwoven” or “nonwoven web” refers to a web of material thatis formed without the aid of a textile weaving or knitting process. Theterm “fabrics” is used to refer to all of the woven, knitted, andnonwoven fibrous webs.

Fibers constituting the nonwoven fabric will typically have a lineardensity of 1.5 to 3.5 denier. The fibers constituting the nonwovenfabric are not particularly limited in form or material provided thefiber diameter falls within the above range. Either continuous filamentsor staple fibers may be used. The individual fibers used to compose thenonwoven fabric may be synthetic, naturally occurring, or a combinationof the two. The fibers include thermoplastic synthetic fibers, such aspolyethylene fibers, polypropylene fibers, polyester fibers andpolyamide fibers; natural fibers, such as cotton, hemp and wool; andregenerated fibers, such as rayon fibers and acetate fibers. Theindividual fibers may be mechanically, chemically, or thermally bondedto each other. The nonwoven fabrics will typically have a basis weightof 10 to 35 g/m². Nonwovens are used commercially for a variety ofapplications including insulation, packaging (e.g., foods such as meat),household wipes, surgical drapes, medical dressings, and in disposablearticles such as diapers, adult incontinent products and sanitarynapkins. Tissue is a closely related material in which the individualfibers may or may not be chemically bonded to one another.

A “liquid-permeable topsheet” generally comprises a nonwoven web; aspunbond, meltblown, or bonded-carded web composed of synthetic polymerfilaments or fibers, such as polypropylene, polyethylene, polyesters orthe like; a perforated film; or a web of natural polymer filaments orfibers such as rayon or cotton.

A “liquid-impermeable backsheet” generally comprises moisture-barriermaterials such as films, wovens, nonwovens, laminates of films, or thelike. For example, the backsheet may comprise a substantiallyliquid-impermeable web or sheet of plastic film such as polyethylene,polypropylene, polyvinyl chloride, or similar material. The backsheetfunctions to contain liquids, such as water, urine, menses, or blood,within the absorbent core of the disposable absorbent product and toprotect bedding and/or a wears' outer garments from soiling. Materialsuseful as a backsheet in a disposable absorbent product are generallyimpermeable to liquid but preferably are permeable to vapor. Examplesare liquid-impervious materials such as polyolefin films, e.g.,polypropylene and polyethylene, as well as vapor-pervious materials,such as microporous polyolefin films, sometimes referred to asbreathable films.

As noted above, some disposable absorbent articles are constructed withvarious types of elasticized waistbands and elasticized leg bands or legcuffs. One method of constructing elasticized regions is to incorporateelastic strands into a laminate that is then attached to a part of thedisposable absorbent product as it is built. For example, elasticstrands have been laminated between layers of polymer film and/or layersof woven or nonwoven fabrics to provide the absorbent product withelastomeric regions. Folded-over layers have also been employed toenclose or envelop selected strands of material. These folded-overlayers have been employed to enclose elastomeric strands within thewaistband, leg cuff and inner barrier cuff components of disposablediapers and other disposable absorbent articles. The polymeric film orfilms, layers of woven or nonwoven fabrics, and/or folded-over layersmay be an integral portion of the topsheet and/or backsheet discussedabove, or may be separate components that are attached to the topsheetand/or backsheet.

In order to introduce an elastic strand to the product being made, aspool of the strand is generally placed on an unwind stand. The strandis then continuously unwound, in the machine direction, with the strandbeing attached to a substrate, such as a base layer of material, toprovide a composite. For purposes of this application, “piece” or“component” encompasses webs such as the aforementioned substrates orbase layers of materials. As stated above, examples of a base materialinclude, but are not limited to, polymeric films and/or woven ornonwoven fabrics. Also, as stated above, the elastic strand is typicallysandwiched between two different layers of base material, or between afolded-over portion of base material, to form a composite. In thepractice of the invention, the strand is advantageously attached to thebase material, or materials, using the adhesive of the invention.

To produce an elasticized region, the strand is stretched when it isattached to a base material to form a substrate composite. The stretchedelastic strands tend to retract and gather the composite, therebyimparting elastomeric properties to the composite. As mentioned above,the composite may be formed to provide an elasticized waistband or legband in a disposable absorbent product.

The adhesive of the invention may be used to attach the topsheet to thebacksheet. Alternatively, the adhesive may be used to adhere either thetopsheet or the backsheet to other components of the disposableabsorbent product, such as tissue layers, leg flaps, fastening ears,tapes, or tabs, or other components typically used to construct adisposable absorbent product that are well known to one skilled in theart.

The adhesive of the invention is particularly useful as an elasticattachment adhesive. Materials with excellent stretchability andelasticity are needed to manufacture a variety of disposal and durablearticles such as, for example, incontinence pads, disposable diapers,training pants, clothing, undergarments, sports apparel, automotivetrim, weather-stripping, gaskets, and furniture upholstery.Stretchability and elasticity are performance attributes that can, forexample, function to effectuate a closely conforming fit to the body ofa wearer or to the frame of an item. While numerous materials are knownto exhibit excellent stress-strain properties and elasticity at roomtemperatures, it is often desirable for elastic materials to provide aconforming or secure fit during repeated use, extensions and retractionsat elevated temperatures such as at body temperatures or in automobileinteriors during summer months. The adhesives find particular use aselastic attachment adhesive for use in non-woven applications such asbaby diaper or adult incontinence items. In addition to the non-wovenmarkets, the hot melt adhesives of the invention are useful in thepackaging, converting and bookbinding markets where the desire is toreduce application temperature and, at the same time, keep the toughnessand strength of the adhesive.

Disposable elastic articles are typically composite materials preparedfrom polymer films, elastomeric fibers, nonwoven sheets and/or absorbentmaterials by a combination of fabrication technologies. Elastomericfibers can be prepared by well known processes such as melt- andsolution-spinning and optionally winding. Nonwoven sheets can beprepared by spun bonding, melt blowing, hydroentangling, mechanicalentangling and the like. Film and sheet forming processes typicallyinvolve known extrusion and coextrusion techniques, e.g., blown film,cast film, profile extrusion, injection molding, extrusion coating, andextrusion sheeting. Polymer films are preferably liquid-imperviousmaterials such as polyolefin films, e.g., polypropylene andpolyethylene, as well as vapor-pervious materials, such as microporouspolyolefin films, sometimes referred to as breathable films.

Durable elastic articles such as, for example, automotive door andwindow trim, clothing waist-band threads or strips, and buildingweather-stripping can be made by well-known molding, thermoforming andprofile extrusion technologies.

A material is typically considered elastomeric when it is characterizedas having a high percent elastic recovery (i.e., a low percent permanentset) after application of a biasing force. Ideally, elastic materialsare characterized by a combination of three, temperature independentproperties, i.e., a low percent permanent set, a low stress or load atstrain, and a low percent stress or load relaxation. That is, thereshould be at low to elevated service temperatures (1) a low stress orload requirement to stretch the material, (2) no or low relaxing of thestress or unloading while the material is stretched, and (3) complete orhigh recovery to original dimensions after the stretching, biasing orstraining is discontinued. Thus, an elastomeric polymer is typically apolymer which, free of diluents, has a break elongation in excess of100% independent of any crimp (when in fiber form) and which whenstretched to twice its length, held for one minute, and then released,retracts to less than 1.5 times its original length within one minute ofbeing released.

Polymers with elastomeric properties include, but are not limited to,natural rubber or synthetic rubbers, segmented polyurethanes (includingpolyurethaneureas) such as polyetherurethanes and polyesterurethanes,polyetheresters, such as for example, Hytrel® from Du Pont, elastomericpolyolefins such as for example elastomeric polypropylene andelastomeric polyethylene for example XLA fibers from Dow, andelastomeric polyamides such as polyetheramides, polyetheresteramides,and polyetheramides for example Pebax® from Atofina. The article of theinvention can comprise substrates containing such elastomeric polymersin various forms, and such substrates can be used in the process of theinvention.

The adhesives of the invention are particularly useful in themanufacture of articles that comprise the adhesive and at least oneelastomeric substrate such as at least one elastomeric fiber, tape,film, strip, coating, ribbon and/or sheet, for example, spandex (e.g.,Lycra® spandex and Lycra® XA, a spandex having little or no lubricatingfinish thereon). In one embodiment, the substrate comprises spandex ormelt spun elastomers. In another embodiment the substrate comprisesnatural or synthetic rubbers in the form of fibers or in the form ofstrips less than about 10 mm wide. The adhesive and at least oneelastomeric substrate may comprise at least one component of an articleof manufacture. Non-limiting examples of such components includewaistbands, leg bands, bellybands, etc.

The U.S. International Trade Commission defines spandex as amanufactured fiber in which the fiber-forming substance is a long-chainsynthetic polymer comprised of at least 85 percent by weight of asegmented polyurethane. Lycra® spandex is known to exhibit nearly ideal,temperature independent elastic properties rendering it very suitablefor use in garments, sports apparel and swimsuits.

The invention is further illustrated by the following non-limitingexamples.

EXAMPLES

In the following examples, all parts are by weight and all temperaturesin degrees Fahrenheit unless otherwise noted.

Adhesive Preparation. All the formulations described herein wereprepared in a 600 g Brabender mixer with sigma blades. The thermoplasticelastomers and about 20% of the oil in the formulation were added to thebowl preheated to about 325° F. Once homogenous, the ionomer was added.Once homogeneous, a mid-block tackifying resin was added. Finallyadditional oil and the end block tackifier were added. The blendingprocess ended when the mixture was homogeneous.

The non-woven substrate used in the examples was a 16.5 g/m² spunbondedpolypropylene manufactured by Avgol.

The polyethylene film used in the examples was a corona treatedTXEM-244.0 embossed film with thickness of 0.75 mil. The film is made byPliant Corp.

The adhesive samples were subjected to the test described below.

Melt viscosities of the hot melt adhesives were determined on aBrookfield Model RVT Thermosel viscometer using a number 27 spindle.

Tensile performance of the hot melt adhesives was determined on 0.125″thick, 2.5″ long dogbone shaped portions with 1×1″ end tabs and a0.5×0.5″ central gage portion. These were pulled on an Instron withpneumatic grips at a speed of 12″/min. and the yield stress and ultimatestress determined.

Mechanical Dynamic Performance of the hot melt adhesive was determinedby a Rheometrics Dynamic Mechanical Analyzer (Model RDA 700) to obtainthe elastic (G′) and loss (G″) moduli versus temperature. The instrumentwas controlled by Rhios software version 4.3.2. Parallel plates 8 mm indiameter and separated by a gap of about 2 mm were used. The sample wasloaded and then cooled to about −100° C., and the time program started.The program test increased the temperature at 5° C. intervals followedby a soak time at each temperature of 10 seconds. The convection ovencontaining the sample was flushed continuously with nitrogen. Thefrequency was maintained at 10 rad/s. The initial strain at the start ofthe test was 0.05% (at the outer edge of the plates). An autostrainoption in the software was used to maintain an accurately measurabletorque throughout the test. The option was configured such that themaximum applied strain allowed by the software was 80%. The autostrainprogram adjusted the strain at each temperature increment if warrantedusing the following procedure. If the torque was below 200 g-cm thestrain was increased by 25% of the current value. If the torque wasabove 1200 g-cm it was decreased by 25% of the current value. At torquesbetween 200 and 1200 g-cm no change in strain was made at thattemperature increment. The shear storage or elastic modulus (G′) and theshear loss modulus (G″) were calculated by the software from the torqueand strain data. Their ratio, G″/G′, also known as the tan delta, wasalso calculated. The mid-block Tg was taken as the maximum in tan delta.

Creep Performance was evaluated by measuring how much a free-end elasticstrand retracts under the stretched condition at end-use temperature(100° F.) during a 4-hour period.

The length of a filament (spandex) adhered in the stretched conditionbetween two nonwoven sheets or a nonwoven sheet and a polymeric film wasmeasured (“starting length”). Both ends of the spandex were cut and theamount that the resulting free-end filament retracts was measuredfollowing a 4 hour period at 100° F. The percent creep was thencalculated in the following manner:

${\%\mspace{14mu}{creep}} = {\frac{{{starting}\mspace{14mu}{length}} - {{final}\mspace{14mu}{length}}}{{starting}\mspace{14mu}{length}} \times 100}$For example, if the initial distance between marks is 20 cm and thefinal distance between the marks is 15 cm, the percent creep is 25%.Five samples for each condition were tested and the results averaged foreach elastic strand and result recorded.

When testing creep performance by either spiral or strand application,the non-woven substrate used was 16.5 gsm spunbond, made by Avgol, thepolyethylene film was TXEM-244.0 embossed with thickness of 0.0007500gauge, corona treated, supplied by Pliant Corp., and the spandex usedwas 620 Decitex (LYCRA®XA®) and the draft of the fiber was 4.0×.

When measuring creep for a bond made through strand coating, adhesivewas applied at a temperature of 275° F. on the nonwoven substrate andspandex with a strand coating pattern in a continuous mode using a highspeed laminator at 300 fpm and an open time of 0.1 sec and an ITW omegaapplicator. The adhesive add on level was 2.5 mg/in with three elasticfibers.

When measuring creep for a bond made through spiral coating, adhesivewas applied at a temperature of 275° F. on the nonwoven substrate andspandex with an unwrapped spiral pattern in an intermittent mode usinghigh speed laminator at 300 fpm with 0.1 sec open time and a Nordson0.018″ spiral applicator. The adhesive add-on level was 8 mg/in withthree elastic fibers being attached to the non-woven substrate.

Example 1

An adhesive was prepared having the formula show in Table 1. Kraton D1124 is a SIS block copolymer with 30% styrene, melt flow index of 4 anddi-block percentage of 30%. Escorez 5400 is a petroleum hydrocarbonresin obtained from Exxon, which has a softening point of 100 to 106° C.Kristallex F115 is alpha-methyl styrene based hydrocarbon resin obtainedfrom Eastman Chemical Company, which has a softening point of 114 to120° C. Nyflex is a mineral oil obtained from Nynas. IRGANOX 1010FF,IRGANOX 565, and IRGANOX PS8000FL are various antioxidants obtained fromCiba Specialty Chemicals Corporation. The amounts in Table 1 are inweight percent based on the total weight of the formulation.

TABLE 1 Sample A Kraton D1124K 20 Escorez 5400 55.8 Kristallex F115 7Nyflex 16.5 IRGANOX 1010FF 0.4 IRGANOX 565 0.1 IRGANOX PS8000FL 0.2

Various properties of formulations listed in Table 1 and the creepperformance (tested between a nonwoven sheet and a polymeric film(NW/Poly)) when they were used as an elastic attachment adhesive withadd-on of 2.5 mg/in for three elastic strands are shown in Table 2. Thefiber used in this example was 620 decitex Lycra® XA® spandex. The draftof the fiber was 4.0× while it was being adhered to the nonwoven. Theadhesive was applied on the nonwoven substrate and spandex with a strandcoating pattern in a continuous mode using a high speed laminator at 300fpm and an open time of 0.1 sec and an Illinois Tool Works (ITW) omegaapplicator. The adhesive was applied at a temperature of 275° F.

TABLE 2 Ultimate Stress (psi) 128 G′ at 40° C. (Pa) 24091 Viscosity at275° F. (cp) 6900 Adhesive Application Temperature (° F.) 275 Yieldstress (psi) 30 NW/Poly Creep Performance (%) 10

Example 2

Adhesives having the formulations shown in Table 3 were prepared. Vector4211 is a tri-block copolymer of styrene and isoprene with isoprene assoft mid-block that is around 30% styrene and has melt flow index around10-16 (ExxonMobil Chemical Company). Eastotac H100R is a hydrogenatedhydrocarbon tackifying resin which has a Ring and Ball softening pointof 95° C. to 105° C. and is available from Eastman Chemical Company.Kristalex® 3085 is an aromatic hydrocarbon resin having a Ring and Ballsoftening point of 82° C. to 88° C. (Eastman Chemical Company). Surlyn9970, Surlyn 8670 and Surlyn 8660 are ethylene-acrylic acidcopolymer-based ionomers available from E.I. duPont de Nemours andCompany. The acid content and percentage of neutralization are differentfor each of these ionomers. Surlyn 8670 and Surlyn 8660 are neutralizedby Na⁺, whereas Surlyn 9970 is neutralized by Zn⁺⁺. Each formulationalso had 0.5% of anti-oxidant (IRGANOX 1010FF) added. The amounts inTable 3 are in weight percent based on the total weight of theformulation.

TABLE 3 Sample B1 Sample B2 Sample B3 Surlyn 8670 3.4 Surlyn 8660 3.4Surlyn 9970 2.0 Vector 4211 13.6 13.6 16.0 Kristalex 3085 8.5 8.5 8.2Eastotac H-100R 59.2 59.2 57.6 Kaydol Oil 15.3 15.3 16.2

Various properties of formulations listed in Table 3 and the creepperformance (tested between two nonwoven sheets (NW/NW) and between anonwoven sheet and a polymeric film (NW/Poly)) when they were used as anelastic attachment adhesive with add-on of 2.5 mg/in for three elasticstrands are shown in Table 4. The fiber used in this example was 620decitex Lycra® XA® spandex. The draft of the fiber was 4.0× while it wasbeing adhered to the nonwoven. The adhesive was applied on the nonwovensubstrate and spandex with a strand coating pattern in a continuous modeusing a high speed laminator at 300 fpm and an open time of 0.1 sec andan ITW omega applicator. The adhesive was applied at a temperature of275° F.

TABLE 4 Sample B1 Sample B2 Sample B3 Ultimate Stress (psi) 112.4 109.0120.3 G′ at 40° C. 2.71 × 10⁴ 2.22 × 10⁴ 2.38 × 10⁴ Viscosity at 275° F.(cp) 4500 4000 4500 Yield stress (psi) 61.0 53.6 29.1 AdhesiveApplication 275 275 275 Temperature (° F.) NW/NW Creep 9.2 10.8 9.0Performance (%) NW/Poly Creep 10.2 11.3 8.5 Performance (%)

This example shows that good creep performance is obtained with anadhesive that can be applied at below 275° F. with strand application.

Example 3

Adhesives having the formulations shown in Table 5 where prepared. Theamounts in Table 5 are in weight percent based on the total weight ofthe formulation.

TABLE 5 Sample C1 Sample C2 SIS block/radial copolymer 16.0 16.0 SBSblock copolymer 2.5 2.5 Surlyn 9970 1.5 1.1 Vinyl aromatic resin 3.0 3.0C5/C9 tackifying resin 60.8 61.2 Mineral Oil 16.2 16.2 Anti-oxidant 0.50.5

Various properties of formulations listed in Table 5 including creepperformance (tested between a nonwoven sheet and a polymeric film(NW/Poly)) are shown in Table 6. The fiber used in this example was 620decitex Lycra® XA® spandex. The draft of the fiber was 4.5× while it wasbeing adhered to the nonwoven. The adhesive was sprayed on the nonwovensubstrate and spandex with a unwrapped spiral pattern in an intermittentmode using high speed laminator at 300 fpm with 0.1 sec open time and aNordson 0.018″ spiral applicator. The adhesive add-on level was 8 mg/inwith three elastic fibers being attached to the non-woven substrate. Theadhesive was applied at temperature of 275° F.

TABLE 6 Sample C1 Sample C2 Ultimate Stress (Psi) 173.2 151.2 G′ at 40°C. 2.77 × 10⁴ 2.89 × 10⁴ Viscosity at 275° F. (cp) 6125 6425 Yieldstress (psi) 68.1 60.0 Adhesive Application Temperature (° F.) 260 270NW/Poly Creep Performance (%) 16.9% 12.1%This example shows that good creep performance is obtained with anadhesive that can be applied at below 275° F. with spiral application.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A low application temperature thermoplastic hot melt adhesivecomprising from about 0.5 to about 55 wt % of a thermoplastic elastomer,from about 30 to about 90 wt % of a tackifying resin, from about 0.1 toabout 40 wt % of an ionomer resin, from 0 to about 40 wt % of a diluentand from 0 to about 25 wt % of a wax, and wherein the adhesive has aviscosity at 275° F. of less than about 8,000 centipose, a yield stressof less than about than 80 psi and a creep performance for a bond madethrough strand coating of less than about 25%.
 2. The adhesive of claim1 comprising from about 0.1 to about 15 wt % of said ionomer resin. 3.The adhesive of claim 2 wherein the thermoplastic elastomer isstyrene-isoprene-styrene, styrene-butadiene-styrene,styrene-b-ethylene/butylene-b-styrene or a mixture thereof.
 4. Anarticle of manufacture comprising the adhesive of claim
 1. 5. Thearticle of claim 4 which is a disposable absorbent article.
 6. Thearticle of claim 5 which is a disposable elastic article.
 7. The articleof claim 6 which is a diaper.
 8. The article of claim 4 wherein thearticle of manufacture further comprises an elastomeric fiber selectedfrom the group consisting of natural rubber, synthetic rubber, spandex,and melt-spun elastomers.
 9. The adhesive of claim 1 which is applied ata temperature of from about 270° F. to about 285° F.